34x34 - I've just spotted the thread (I have the GPS board on ignore).
I've been poking at this for just over a year, but I only took it moderately seriously after Si S mentioned he was trying to chase me down
I've been more opportunistic than systematic in my square-bagging, as I like to make it a decent ride. So my cluster's up to a healthy 2503, and snakes about all over the place. All the squares at the edges of my square are going to be tricky to get - trackless moors, Hartlepool Bay (though I'm convinced I can wait until low tide and walk out across the rocks to get that one), and an annoying square between Thirsk and Topcliffe - it looks like the only way to get it is hacking along the A168, which looks like a 2 am job to me.
I've loads of easy squares with lots of roads around East Durham, but see the point above about wanting to have a decent ride.
I can't remember where I heard about it - I think I just spotted it as a metric on Veloviewer, and followed it on from there. The most satisfying squares have been the ones in some of the many military ranges around Catterick - it took me three or four goes before I managed to cross Feldom Ranges, as the flags were alway up. I've lost count of the number of abandoned (or active) airfields I've snuck into, and I even stumped up cash to get into Raby Castle grounds to bag the three squares at the back of there - where you're not meant to go.
It's at least a 50-mile round trip to get any more now, though, and that probably means overnight bivvies or something equally daft. And then, if I keep going, in a year or so, I'll hit Warcop Ranges. Which is fucking enormous.